Biaxial orientation blow-molded bottle made of a synthetic resin, especially biaxial orientation blow-molded bottle of a polyethylene terephthalate resin are used in many fields and in large numbers as bottle containers, because they exhibit a number of excellent features.
This biaxial orientation blow-molded bottle of a synthetic resin is generally manufactured by biaxially drawing in the axial direction and in the radial direction and blow-molding a preform, which has been injection-molded into a bottomed cylindrical shape, while heating it to a temperature capable of developing the orientation effect.
According to a method of the prior art, as described in JP-A-1995-290562 and shown in FIG. 14, a preform P, which is so held by a holding jig 5 as is loosely fitted in an inverted posture by a guide cylinder member 10 and which is heated to a temperature capable of the drawing effect, is assembled with a blow mold 1 together with the holding jig 5 such that a neck ring P1 formed integrally with and circumferentially of the lower end of the outer circumference of a mouth cylinder portion P2 of the preform P is retained on a neck supporting flanged portion. 3 of the blow mold 1. The preform P is axially drawn and molded in the axial direction by a drawing pin 16, which is inserted into a pin inserting bore 11 formed through in the center of the holding jig 5, and is drawn and molded in the radial direction with the blow air, which is pumped in through the pin inserting bore 11 or the drawing pin 16, so that a bottle P′ is molded.
In the method of the prior art described above, the posture of the preform is loosely retained mainly by the guide cylinder member 10.
In JP-A-1997-314650, for example, there is described a double blow molding method. This method includes: the step of biaxial orientation blow molding the preform into a primary intermediate molding; the step of heating and thermally shrinking the primary intermediate molding into a secondary intermediate molding; and the final step of blow molding the secondary intermediate molding into a bottle. The bottle manufactured can have little residual strain and a high heat resistance.
In the method of the prior art, however, especially with the holding jig being detached from the blow mold, the preform is just loosely fitted at its mouth cylinder portion in the holding jig. There arise problems that the posture is broken while the preform is being transferred, to cause production troubles., and that the posture of the secondary intermediate molding being heated during the double blow molding is deflected to cause defective phenomena such as the bite of the mold.
According to the method of the prior art in which the assembled posture of the preform is held by inserting the guide cylinder portion into the mouth cylinder portion of the preform, moreover, that effective sectional area of the inside of the mouth cylinder portion of the preform, which can be utilized as a passage for the blow air, is reduced to raise a problem that it is impossible to achieve the improvement in productivity, which has been intended by increasing the flow rate of blow air to shorten the blow time period.
Just after the blow molding, moreover, there are found many steps of cooling the bottle by an air circulation to blow air into the bottle. These steps are executed mainly through an air passage formed in the drawing pin. However, there is a desire to enlarge the air passage, to increase the air flow rate, to raise the cooling efficiency thereby to improve the productivity better. The reduction in the effective sectional area of the mouth cylinder portion also raises a problem against those demands.
Therefore, the present invention has been conceived to solve the aforementioned problems of the prior art, and has a technical object to hold a preform stably in an assembled posture thereby to achieve a safe and high productivity of the biaxial orientation blow-molded bottle.
Another technical object is to enlarge the passage of air into the preform thereby to achieve a high productivity of the biaxial orientation blow-molded bottle.